Typically, the semiconductor chips are presented on a foil held in a frame, also known in the trade as a tape, for processing with such a mounting apparatus. The semiconductor chips adhere to the foil. The frame with the foil is accommodated by a movable wafer table. The wafer table is shifted in cycles so that one semiconductor chip after the other is presented at a first location A and then the presented semiconductor chip is picked up by a chip gripper and placed at a second location B on a substrate. Removal of the presented semiconductor chip from the foil is supported by a chip ejector (known in the trade as a die ejector) arranged underneath the foil. In doing so, as a rule at least one needle arranged in the chip ejector supports detachment of the semiconductor chip from the foil.
From the U.S. Pat. No. 4,921,564, a method has become known with which the semiconductor chips can be detached from the foil and picked up by the chip gripper without the aid of a needle. With this method, the foil with the semiconductor chips is placed onto a heatable plate. On the side facing towards the foil, the plate has cavities to which vacuum can be applied. When mounting, on the one hand vacuum is applied to the cavities so that the foil is pulled into the cavities and is partly detached from the semiconductor chips. On the other hand, in order to additionally reduce the adhesion of the semiconductor chips to the foil, the foil is heated to a temperature of 50° C. to 65° C. This method works for numerous semiconductor chips however, with comparatively large but very thin semiconductor chips, it often happens that, on applying the vacuum and removing the foil, the semiconductor chips lift and then fall back onto the foil whereby it can also happen that adjacent semiconductor chips overlap.
The thickness of the semiconductor chips to be detached continuously decreases. Today, in many cases the thickness already only amounts to 100 micrometers with the trend to further reduced thicknesses of 75 to 50 micrometers. In addition to this, there is an adhesive layer on the back of the wafers. The adhesion of the semiconductor chips on the wafer is therefore increased. The technology described above with which the semiconductor chips are detached with the aid of needles is reaching its limits. The detachment of the foil with vacuum in accordance with U.S. Pat. No. 4,921,564 also doesn't work any more: the foil can no longer be heated to the required temperature of 50° C. to 65° C. because at these temperatures the adhesive layer hardens so that the semiconductor chips adhere even better to the foil.
A further method for detaching a semiconductor chip from a foil is known from U.S. Pat. No. 6,561,743. With this method, the foil with the semiconductor chip to be detached is pulled over an edge whereby the semiconductor chip and the foil are detached from each other on the edge. Detachment of the foil is stopped before the semiconductor chip has completely detached itself from the foil. In order to control detachment of the semiconductor chip from the foil, the chip gripper is first lowered onto the semiconductor chip and vacuum is applied to the semiconductor chip. The foil is then pulled over the edge until the semiconductor chip has completely detached itself from the foil. A similar method is known from U.S. Patent Application Publication No. 2002/0129899. These methods have the disadvantage that adjacent semiconductor chips can be damaged because the height of the edge necessary for detachment has to be about 1.5 millimeters.
An object of the present invention is to develop a robust method for the detachment of semiconductor chips from a foil with which adjacent semiconductor chips are not damaged.